The present invention relates to the art of electrochemically removing undesirable or harmful metal deposits from ferrous base metals and, in a principal embodiment, the invention pertains to a method and apparatus for electrochemically removing from the bores of firearms metal bullet fouling which is deposited therein.
The metal deposits and other residues left in the bores and other interior parts of firearms as a result of the firing of bullets or other types of ammunition must be periodically removed. The firing of both percussive and non-percussive ammunition results in the deposit on the bore of a firearm or gun system of a layer of metal from the projectiles, as well as carbon and other fouling from the gunpowder or firing charge. If the fouling is not periodically removed, the accuracy or function of the firearm and the integrity of the ferrous metal bore and other interior parts will be adversely affected.
Bore cleaning methods are well established in the prior art and, in general, include various combinations of mechanical abrasion and chemical oxidation or dissolution of the fouling. The methods, apparatus and chemicals used have changed very little in a century or more and the basic process is characterized by tedious and time-consuming work. Also, many of the cleaning solvents used pose significant health hazards because of their volatility and/or toxicity. Furthermore, similar prior art methods and materials have been used both for conventional firearms, like those used for hunting and target shooting, and larger or more sophisticated weapons, such as those used in military or police applications.
Metal fouling is the most difficult of the foulant materials to remove from the bore of a firearm. Metal fouling may comprise a layer of lead or lead alloy from firing lead or partially-jacketed bullets; or copper, gilding metal or other copper alloy metals from jacketed bullets. The layer of metal fouling is most commonly removed by wetting the interior of the bore with a solvent or penetrant which dissolves or loosens the metal fouling. Various types of brushes are frequently used to aid loosening. The residue is then removed from the bore with a cloth patch on a cleaning rod. For harder or thicker metal layers, abrasive cleaners applied with a patch or metal-bristled brush, with or without solvents, are often used. In cases of severe lead fouling, medium-fine steel wool, wound around a brass-bristled brush, has been recommended.
In another method for removing copper or copper alloy fouling, a firearm may be placed muzzle up, the chamber end of the bore plugged, the barrel filled with an aqueous ammonia solution and allowed to stand for several hours until the metal fouling is chemically oxidized and dissolved. The bore is then brushed and swabbed as discussed above. However, the ammonia concentration in some formulations is sufficiently high that contact with the eyes is dangerous and the evolution of noxious fumes inhibits indoor use. Also, in instances of heavy fouling, multiple treatments of this type may be required.
One other prior art method used to remove lead fouling involves treating the bore with mercury to form a lead-mercury amalgam which loosens and/or dissolves the lead from the bore for relatively easy removal. However, the high toxicity and hazards related to the handling and use of mercury are well known and this method is, therefore, extremely unsafe, regardless of its efficacy.
Repeated cleaning of firearms by the foregoing methods, particularly those using abrasive brushing, are known to measurably wear the precision bore surfaces, adversely affect performance and accuracy, and result in shorter useful life. The potential damage to firearms resulting from necessarily severe abrasive cleaning of heavily leaded bores is well documented, as is the absence of safe and effective alternate methods. See, for example, E. H. Harrison, "Cast Bullets," National Rifle Association, 1979, p. 33; and, "Reloading Manual Number Ten for Rifle and Pistol," Omark Industries, Inc., 1979, p. 364.
U.S. Pat. No. 1,050,678 describes an embodiment of one of the foregoing processes using aqueous ammonia or methylamine in the presence of air. U.S. Pat. No. 1,484,690 discloses the use of a bore cleaning mixture of ammonium persulfate, ammonium sulfate and an alkali in aqueous solution to remove copper or cupro-nickel fouling. However, ammonia-based solutions are most commonly used today and little if any improvement has been made in this tedious and time-consuming process since its first use three-quarters of a century ago.
U.S. Pat. No. 1,050,678 also discusses the use of electrolysis to remove copper fouling from gun bores, but discloses no specific method and dismisses its use generally because of electrochemical attack on the base metal of the gun barrel (page 1, lines 68-83). The inventors herein are aware of no other prior art disclosing the use of electrochemical cleaning processes for the selective removal of gun bore metal fouling.
The prior art also discloses various methods for electrolytically stripping nonferrous metal coatings from ferrous base metals. U.S. Pat. No. 2,561,222 describes a method of stripping lead, copper, zinc and other metal electrodeposits from ferrous base metals in an electrolytic bath consisting of sodium nitrate and chromic acid and with controlled current densities at the coated ferrous metal positive electrode in the range of 1/4 to 4 amps/in..sup.2. Although the method purports to avoid excessive attack on the ferrous base metal, the electrolytic action is described as producing an appreciable smoothing of the ferrous base by removing small burrs and projections. The disclosed electrolyte is in fact highly oxidizing to iron and, at the current densities applied, would result in totally unacceptable corrosion of the rifling and surfaces of the steel bore of a firearm, particularly if used repeatedly.
A similar electrolytic stripping process is disclosed in U.S. Pat. No. 2,581,490 wherein copper, nickel, or chromium coatings are removed in a bath consisting of sodium nitrate and an alkali metal hydroxide to which sodium nitrite is added to prevent etching of the ferrous base metal. However, the disclosed electrolytic solution is also highly oxidizing and, although its use may be wholly acceptable for processing commercial steel sheet, it would be unacceptable for use on the precision bores of firearms. In addition, the process operates at relatively high current densities and temperatures and requires the use of chemicals which pose substantial health hazards.
Thus, the prior art discloses no processes or methods for eliminating or alleviating the tedious, time-consuming and sometimes hazardous task of removing metal fouling from the bores of firearms. There is, as a result, a need for a simple, convenient and fast method for removing metal fouling which is neither hazardous to the user nor harmful to the precision surfaces of the firearms.
It is also known that metal fouling or contamination is a serious problem in certain precision molding and casting arts. For example, in the art of powder metallurgy, adherent metal powder deposits on the mold surfaces must be periodically removed and, likewise in the die casting art, so-called "soldering" of cast metal deposits on internal die surfaces presents similar problems. Not only does contamination of precision molds and dies with metal from the formed parts result in unacceptable dimensional variations, but cleaning such metal deposits is typically done manually with abrasives, is tedious, and must be done with great care to avoid damaging the dies and molds themselves. A simple, safe and effective method for cleaning precision dies and molds is, therefore, most desirable.